Integrated circuit package and a method for dissipating heat in an integrated circuit package

ABSTRACT

An IC package that is suitable for surface mounting arrangements includes a heat spreader device that is coupled to a bottom portion of the package below the IC die. Coupling the heat spreader device to the bottom portion of the package reduces or eliminates the possibility that placement of the heat spreader device will result in the molding compound bleeding on top of the heat spreader device, and delamination at the footings of the heat spreader device that can cause the package to delaminate, or “popcorn”.

TECHNICAL FIELD OF THE INVENTION

The invention relates to integrated circuits (ICs). More particularly,the invention relates to a method and an apparatus for dissipating heatin an IC package.

BACKGROUND OF THE INVENTION

For packaged IC devices that are intended for use as surface mountdevices, the current technique for dissipating heat in the packageinvolves using a heat spreader device that is coupled to a top portionof the IC device. FIG. 1 illustrates a side cross-sectional view of apackaged IC device 2 positioned between top and bottom mold plates 3 and4, respectively. The IC package 2 has a die 5 that is attached by a dieattach material 6 to a die attach region 7 of a substrate 8 of aleadframe 11. Pads (not shown) on the die 5 are connected by electricalconductors (e.g., gold wires) 9 to the leadframe 11 of the package 2. Aheat spreader device 3 extends over a top portion of the package 2 abovethe die 5 and has footings that are attached by an attachment materialto the leadframe 11. The heat spreader device 12 is separated from thedie 5 by a molding compound 13. When the molding compound 13 is cured,it solidifies and secures the heat spreader device 3 in the positiondepicted in FIG. 1.

The heat spreader device 3 must be precisely positioned on the topportion of the IC device 2 before the package is molded (i.e.,encapsulated). If the heat spreader device 12 is not preciselypositioned on the device 2 when the molding process is performed, themolding compound 13 may bleed or run (i.e., flow onto the top of theheat spreader device 12). Excessive mold bleed may impede the thermaldissipation property of the IC device 2. In addition, during moldclamping, there is a likelihood that the mold clamp will press onto theheat spreader device 12, which may result in delamination at thefootings of the heat spreader device 12. Moisture may subsequently betrapped in the delaminated regions around the footings of the heatspreader device 12 that might, in turn, result in “pop corning”. “Popcorning” can lead to mechanical damage to the IC device and prevent itfrom operating properly.

FIG. 2 illustrates a flowchart that represents the current assemblyprocess for packaging the IC device shown in FIG. 1 and preparing it formounting via SMT to a printed circuit board (PCB). A wafer having manyIC dies is subjected to a back grinding process during which the waferis thinned, as indicated by block 21. Thinning the wafer reduces thefinal IC package size and lowers the thermal resistance of the final ICpackage. The wafer is then diced into individual dies, as indicated byblock 22. The die is then attached to the leadframe substrate with apaste during a die attach process, as indicated by block 23. The dieattach paste is then cured, as indicated by block 24. The pads of thedie are then bonded to the conductors of the leadframe during a wirebonding process, as indicated by block 25. The heat spreader device isthen attached, as indicated by block 26. Attaching the heat spreaderdevice involves placing an attachment material at particular locationson the leadframe, and precisely positioning the heat spreader deviceabove the die such that the feet of the legs of the heat spreader deviceare in contact with the attachment material. The attachment material isthen cured, as indicated by block 27, which secures the feet of the legsof the heat spreader device to the leadframe. The IC device is thensubjected to the molding process, as indicated by block 28.

After the molding process has been performed, the package is typicallysubjected to a laser marking process that marks the package with someindicia (e.g., part name and number), as indicated by block 29. Thepackage is then subjected to a post-mold curing process, as indicated byblock 31. When used in SMT, the package leadframe is typically nextsubjected to a solder ball mounting process, as indicated by block 32,which places solder balls on the leadframe that will subsequently beused to solder the leadframe to a PCB. A singulation process is thenperformed, as indicated by block 33, which separates the leadframe ofthe IC package from the other leadframes intended to be connected toother like IC devices to form other like IC packages. The IC packageleadframe is now ready to be connected via soldering to a PCB during asubsequent mounting process (not shown).

As described above, if the heat spreader device is not preciselypositioned before the molding process (block 8) begins, the moldingcompound (e.g., resin) may bleed or run during the molding process,which may impede the thermal dissipation performance of the package. Theclamp force acting on the heat spreader device may also lead todelamination on the footings of the heat spreader device which mightlead to “pop corning” at some later time (e.g., during solder ball mountreflow or after it has been mounted to the PCB).

Another technique that has been proposed to prevent this problem is touse a molding compound that has a high thermal conductivity. Using amold compound of high thermal conductivity can improve the thermalperformance of the device. Using this compound, however, usually resultsin a high degree of wire sway occurring during the molding process andhigh package warp. A high degree of warp will result in processingdifficulties, such as ball short, for example, during mounting of the ICdevice to the PCB. This technique has not fully matured and has not beenwidely adopted in the IC fabrication industry.

Accordingly, a need exists for a way to incorporate a heat spreaderdevice into an IC device that obviates problems such as mold bleed,delamination, a high degree of wire sweep, and a high degree of warpingof the final IC package.

SUMMARY OF THE INVENTION

The invention provides an IC package and a method for dissipating heatin an IC package. The IC package comprises a substrate, an IC die, and aheat spreader device. The substrate has a top surface and a bottomsurface and an opening formed therein. The IC die has a top surface anda bottom surface. The top surface of the die has one or more conductivepads disposed on it. The top surface of the heat spreader device iscoupled to the bottom surface and substantially covers the openingformed in the substrate and is coupled with or adjacent to the bottomsurface of the die.

In accordance with one embodiment, the method comprises forming anopening in a substrate at a die placement location, and coupling a topsurface of a heat spreader device to a bottom surface of the substrateadjacent the opening.

In accordance with another embodiment, the method comprises forming anopening in a substrate at a die placement location, covering the openingand at least a portion of a bottom surface of the substrate with anadhesive tape material, subsequent to covering the opening and bottomsurface of the substrate with the adhesive tape material, removing thetape material, and placing a top surface of a heat spreader device incontact with the adhesive material on the bottom surface of thesubstrate such that when the adhesive material cures, the top surface ofthe heat spreader device is coupled to the bottom surface of thesubstrate.

These and other features and advantages of the invention will becomeapparent from the following description, drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a side cross-sectional view of a known IC devicepositioned between top and bottom mold plates during an assemblyprocess, and having a heat spreader device attached to a top portionthereof.

FIG. 2 illustrates a flowchart that represents the current assemblyprocess for creating the IC package shown in FIG. 1 and preparing it tobe mounted via SMT to a PCB.

FIG. 3 illustrates a side cross-sectional view of a packaged IC devicein accordance with an illustrative embodiment of the invention having aheat spreader device coupled to a bottom portion thereof.

FIG. 4 illustrates a flowchart that represents the assembly process ofthe invention in accordance with an illustrative embodiment forpackaging an IC and preparing it to be mounted via SMT to a PCB.

FIG. 5 illustrates a flowchart that represents the process of theinvention in accordance with one illustrative embodiment for forming anopening in a substrate and coupling a heat spreader device to the bottomsurface of the substrate below the opening.

FIG. 6 illustrates a flowchart that represents the assembly process forpackaging an IC device and preparing it to be mounted via SMT to a PCBin accordance with an illustrative embodiment of the invention.

FIG. 7 illustrates a flowchart that represents the process of theinvention in accordance with one illustrative embodiment for pre-tapingthe bottom surface of the substrate and forming an opening in thesubstrate.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In accordance with the invention, an IC package that is suitable forsurface mounting arrangements includes a heat spreader device that iscoupled to a bottom portion of the package below the IC die. Securingthe heat spreader device to the bottom portion of the package reduces oreliminates the possibility that placement of the heat spreader devicewill result in the molding compound bleeding on top of the heat spreaderdevice or delamination at the footings of the heat spreader device,which can cause the package to “popcorn”. The heat spreader device maybe coupled to the package prior to or subsequent to the molding processbeing performed, as will now be described with reference to a fewillustrative embodiments of the invention.

FIG. 3 illustrates a cross-sectional view of an IC package 30 inaccordance with an illustrative embodiment being subjected to a moldingprocess. The package 30 is similar to the package 2 shown in FIG. 1 inthat it includes a die 31 that is coupled by a die attach material 32 toa substrate 34 of a leadframe 36, and pads (not shown) that areconnected by electrical conductors (e.g., gold wires) 35 to conductors(not shown) of a leadframe 36. The substrate 34 of the leadframe 36functions as an insulating layer for insulating the die 31 from theconductors of the leadframe 36. In accordance with the invention, thepackage 30 includes a heat spreader device 40 that is coupled to abottom portion of the package 30.

In accordance with this embodiment, the heat spreader device 40 iscoupled at some time prior to the molding process being performedadjacent the die 31. The substrate 34 has an opening formed therein atthe bottom portion of the package 30, and the die 31 is in contact withthe heat spreader device 40 over the region 50 where the die 31 and theheat spreader device 40 interface with this opening.

Outer portions 41 of the heat spreader device 40 are coupled by someattachment device or material (not shown) to the leadframe 36 to providea thermal path from the die 31 to the leadframe 36 for heat dissipation.The inner surface of the top mold plate 43 is in contact with moldingcompound 45, which is contact with the die 31 and other portions of thepackage 30. The inner surface of the bottom mold plate 44 is not incontact with the molding compound 45, but is in contact with the heatspreader device 40 and other portions of the package 30. The innersurface of the bottom mold plate 44 is shaped to match the shape of thebottom surface of the heat spreader device 40 and other portions of thepackage 30 that the inner surface of the mold plate 44 abuts during themolding process. Thus, the placement of the heat spreader device 40 hasno affect on the molding compound 45 and thus will not result moldbleed.

FIG. 4 illustrates a flowchart that represents the assembly process ofthe invention in accordance with an illustrative embodiment forpackaging an IC and preparing it to be mounted via SMT to a PCB. Theflowchart shown in FIG. 4 is identical to the flowchart shown in FIG. 2except that blocks 26 and 27 in FIG. 2, which are associated withcoupling the heat spreader device and curing the attachment material,have been eliminated. This is because, in accordance with thisembodiment of the invention, the heat spreader device is coupled priorto the assembly process being performed. Blocks 51-55 shown in FIG. 4correspond, respectively, to blocks 21-25 shown in FIG. 2. Likewise,blocks 58-63 shown in FIG. 4 correspond, respectively, to hocks 28-33shown in FIG. 2.

FIG. 5 illustrates a flowchart that represents the process of theinvention in accordance with one illustrative embodiment for forming anopening in a substrate of an IC device and coupling a heat spreaderdevice to the bottom surface of the substrate below the opening. Anopening is formed in a substrate of an IC device on a bottom portion ofthe IC device at a die placement location, as indicated by block 70.This may be performed at the wafer level or at the die level. If theprocess represented by block 70 is performed as part of the assemblyprocess represented by FIG. 4, the openings could be formed, forexample, after the backgrinding process corresponding to block 51 hasbeen performed, but before the dicing process represented by block 52 isperformed. Alternatively, the openings may be performed, for example,after the wire bonding process represented by block 55 has beenperformed, but before the molding process represented by block 58 hasbeen performed. The invention is not limited with regard to when theopening is formed.

After the opening in the substrate has been formed, the heat spreaderdevice is coupled to the bottom surface of the substrate, as indicatedby block 80. This is typically accomplished by placing an attachmentmaterial, such as an adhesive film, on the bottom surface of thesubstrate and/or on the top surface of the heat spreader device. The topsurface of the heat spreader device is then placed in abutment with thebottom surface of the substrate and the attachment material is cured,thereby bonding the top surface of the heat spreader device to thebottom surface of the substrate.

If the process represented by block 80 is performed as part of theassembly process represented by FIG. 4, the heat spreader device may becoupled, for example, after the wire bonding process represented byblock 55 has been performed, but before the molding process representedby block 58 has been performed. The invention is not limited with regardto when the heat spreader device is coupled. If, however, the heatspreader device is coupled prior to the assembly process represented byFIG. 4 being performed, or during the performance of the assemblyprocess, but before the molding process is performed, the possibility ofmold bleed occurring is greatly reduced or eliminated altogether. Theheat spreader device can be precisely positioned on the bottom surfaceof the substrate and coupled by a film adhesive prior to the moldingprocess being performed. Subsequently, the die is coupled through theopening formed in the substrate directly to the top surface of the heatspreader device during the die attach process represented by blocks 53and 54.

Regardless of when the heat spreader device is coupled, positioning theheat spreader device below the die in accordance with the inventiongreatly reduces the length of the thermal path from the die to the heatspreader device in comparison to the length of the thermal path from thedie to the heat spreader device when it is located above the die asdepicted in FIG. 1. It is not necessary for the die to be seateddirectly on the top surface of the heat spreader device, although thisis desirable in that it minimizes the length of the thermal path fromthe die to the heat spreader device. Rather, the size of the opening maybe slightly smaller than the size of the die such that the die sits onthe top surface of the substrate and is separated from the top surfaceof the heat spreader device by a distance equal to the thickness of thesubstrate where the opening is formed. In the latter case, a material ofhigh thermal conductivity may be located within the opening and incontact with the bottom surface of the die and the top surface of theheat spreader device. Both of these arrangements greatly reduce thelength of the thermal path from the die to the heat spreader devicelocated below the die in comparison to the length of the thermal pathwhen the heat spreader device is located above the die as depicted inFIG. 1.

It should also be noted that it is not necessary that the opening beformed prior to the heat spreader device being coupled. The heatspreader device may be coupled prior to the opening being formed in thesubstrate. Thus, the order of the blocks 70 and 80 may be the reverse ofthe order depicted in FIG. 5.

FIG. 6 illustrates a flowchart that represents the assembly process forpackaging an IC device and preparing it to be mounted via SMT to a PCBin accordance with an illustrative embodiment of the invention. Theflowchart shown in FIG. 6 is identical to the flowchart shown in FIG. 4except that block 59 has been added to represent the process of removinga tape removal and blocks 82 and 83 have been added to represent theprocess of coupling the heat spreader device and curing the attachmentmaterial. This is because, in accordance with this embodiment of theinvention, the heat spreader device is coupled after the molding processhas been performed, and preferably after the singulation process hasbeen performed. In accordance with this embodiment, the bottom surfaceof the substrate 34 is pre-taped by laminating the bottom surface of thesubstrate 34 with an adhesive tape material. Using the adhesive tapematerial is advantageous because it allows the die to be directlyattached to the tape material prior to the molding process (block 58).This pre-taping process may be performed at the wafer level or at thedie level. The invention is not limited with regard to when thesubstrate is pre-taped.

After the molding process represented by block 58 has been performed,the tape material is removed, leaving an adhesive material on the bottomsurface of the substrate and die, as indicated by block 59. After thesingulation process represented by block 64 has been performed, the topsurface of the heat spreader device is placed in contact with theadhesive material located on the bottom surface of the substrate anddie, as indicated by block 82. The adhesive attachment material is thencured, as indicated by block 83, which couples the heat spreader deviceto the substrate. The invention is not limited with regard to when thesteps represented by blocks 59, 82 and 83 are performed. By performingthese steps after the molding process has been performed, thepossibility of mold bleed occurring is reduced or eliminated.

FIG. 7 illustrates a flowchart that represents the process of theinvention in accordance with one illustrative embodiment for pre-tapingthe bottom surface of the substrate and forming an opening in thesubstrate. An opening is formed in a substrate of an IC device on abottom portion of the IC device, as indicated by block 110. This openingis formed at the die placement location. The opening may be performed atthe wafer level prior to the assembly process or at the die level duringthe package assembly process. The die may or may not have already beenattached to the substrate when the opening is formed in the substrate.For example, the openings could be formed after the backgrinding processcorresponding to block 51 has been performed, but prior to the dicingprocess represented by block 52 being performed. Alternatively, theopenings may be performed, for example, after the wire bonding processrepresented by block 55 has been performed, but before the moldingprocess represented by block 58 has been performed. The invention is notlimited with regard to when the opening is formed.

After the opening in the substrate has been formed, the adhesive tapematerial is placed on the bottom surface of the substrate, as indicatedby block 120. It should be noted that it is not necessary that theopening be formed prior to the pre-taping process being performed. Theopening may be formed after the pre-taping process has been performed.Thus, the order of the blocks 110 and 120 may be reversed in relation tothe order depicted in FIG. 7.

It should be noted that the invention has been described with referenceto a few illustrative embodiments for the purposes of demonstrating theprinciples and concepts of the invention. The invention is not limitedto these embodiments. Modifications may be made to the embodimentsdescribed herein and all such modifications are within the scope of theinvention.

1. An integrated circuit (IC) package manufacturing system comprising: afirst mold plate; a second mold plate; a substrate having a top surfaceand a bottom surface, the substrate having an opening formed therein andpositioned between the first mold plate and the second mold plate; an ICdie having a top surface and a bottom surface, the top surface of thedie having one or more conductive pads disposed thereon; and a heatspreader device having a top surface, the top surface of the heatspreader device being coupled to the bottom surface of the substrate,wherein the heat spreader device covers the opening formed in thesubstrate and is coupled with or adjacent to the bottom surface of thedie, the second mold plate comprising a space for receiving the heatspreader device such that the top surface of the heat spreader device issubstantially parallel with a top surface of the second mold plate. 2.The IC package manufacturing system of claim 1, further comprising: aleadframe having a top side and a bottom side and one or more conductiveleads; one or more conductors having first ends connected to said one ormore conductive pads disposed on the top surface of the die and havingsecond ends connected to said one or more conductive leads on the topside of the leadframe; and a molding compound in contact with andcovering at least the top surface of the die and said one or moreconductors.
 3. The IC package manufacturing system of claim 2, whereinthe bottom surface of the die is coupled to the top surface of the heatspreader device.
 4. The IC package manufacturing system of claim 2,wherein the bottom surface of the die is coupled to the top surface ofthe substrate adjacent the opening such that the top surface of the heatspreader device is adjacent to the bottom surface of the die.
 5. The ICpackage manufacturing system of claim 2, further comprising: a solderball mounting configuration coupled to the bottom side of the leadframefor allowing the bottom side of the leadframe to be coupled to a circuitboard.
 6. A method for making a system for dissipating heat in anintegrated circuit (IC) package, the method comprising: providing afirst mold plate; providing a second mold plate; forming a space withinthe second mold plate; placing a heat spreader device within the spaceof the second mold plate such that a top surface of the heat spreaderdevice is substantially parallel with a top surface of the second moldplate; forming an opening in a substrate at a die placement location;positioning the substrate between the first and second mold plates; andcoupling the top surface of a heat spreader device to a bottom surfaceof the substrate adjacent the opening.
 7. The method of claim 6, furthercomprising: performing a die attach process, wherein during the dieattach process, a bottom surface of an IC die is coupled to the topsurface of the heat spreader device through the opening formed in thesubstrate.
 8. The method of claim 6, further comprising: performing adie attach process, wherein during the die attach process, a portion ofa bottom surface of an IC die is coupled to a top surface of thesubstrate over the opening such that a portion of the bottom surface ofthe die is disposed in the opening above the top surface of the heatspreader device.
 9. The method of claim 7, further comprising:performing a bonding process, wherein during the bonding process, firstends of one or more conductors are connected to one or more conductivepads on a top surface of the die and second ends of said one or moreconductors are connected to one or more conductive leads of a leadframe;and performing a molding process, wherein during the molding process, atleast the top surface of the die and said one or more conductors arecovered with a molding compound and one or more molding plates are usedto mold the compound.
 10. The method of claim 9, wherein the top surfaceof the heat spreader device is coupled to the bottom surface of thesubstrate prior to the molding process being performed.
 11. The methodof claim 10, wherein the top surface of the heat spreader device iscoupled to the bottom surface of the substrate prior to the bondingprocess being performed.
 12. The method of claim 11, wherein the topsurface of the heat spreader device is coupled to the bottom surface ofthe substrate prior to the die attach process being performed.
 13. Themethod of claim 9, wherein the top surface of the heat spreader deviceis coupled to the bottom surface of the substrate prior to the moldingprocess being performed and subsequent to the die attach process beingperformed.
 14. The method of claim 10, wherein the top surface of theheat spreader device is attached to the bottom surface of the substrateprior to the molding process being performed and subsequent to thebonding process being performed.
 15. The method of claim 7, wherein theopening is formed in the substrate prior to the heat spreader devicebeing attached to the substrate.
 16. The method of claim 7, wherein theopening is formed in the substrate subsequent to the heat spreaderdevice being attached to the substrate.
 17. A method for forming asystem for dissipating heat in an integrated circuit (IC) package, themethod comprising: providing a first mold plate; providing a second moldplate; forming a space within the second mold plate; placing a heatspreader device within the space of the second mold plate such that atop surface of the heat spreader device is substantially parallel with atop surface of the second mold plate; forming an opening in a substrateat a die placement location; covering the opening and at least a portionof a bottom surface of the substrate with an adhesive tape material;subsequent to covering the opening and bottom surface of the substratewith the adhesive tape material, removing the tape material, whereinremoving the tape material leaves an adhesive material on at least aportion of the bottom surface of the substrate; positioning thesubstrate between the first and second mold plates; and placing a topsurface of a heat spreader device in contact with the adhesive materialon the bottom surface of the substrate such that when the adhesivematerial cures, the top surface of the heat spreader device is coupledto the bottom surface of the substrate.
 18. The method of claim 17,further comprising: performing a die attach process, wherein during thedie attach process, a, bottom surface of the IC die is coupled to thetop surface of the heat spreader device through the opening formed inthe substrate.
 19. The method of claim 17, further comprising:performing a die attach process, wherein during the die attach process,a portion of a bottom surface of an IC die is coupled to a top surfaceof the substrate over the opening such that a portion of the bottomsurface of the die is disposed in the opening above the top surface ofthe heat spreader device.
 20. The method of claim 18, furthercomprising: performing a bonding process, wherein during the bondingprocess, first ends of one or more conductors are connected to one ormore conductive pads on a top surface of the die and second ends of saidone or more conductors are connected to one or more conductive leads ofa leadframe; and performing a molding process, wherein during themolding process at least the top surface of the die and said one or moreconductors are covered with a molding compound and one or more moldingplates are used to mold the compound.
 21. The method of claim 20,wherein the tape material is removed and the top surface of the heatspreader device is coupled to the bottom surface of the substratesubsequent to the molding process being performed.
 22. The method ofclaim 20, wherein the tape material is removed and the top surface ofthe heat spreader device is coupled to the bottom surface of thesubstrate prior to the molding process being performed.
 23. The methodof claim 20, wherein the tape material is removed and the top surface ofthe heat spreader device is coupled to the bottom surface of thesubstrate subsequent to the die attach process being performed.